The research proposed in this application will investigate the connection between statistical learning and vocabulary development. Statistical learning refers to the process of detecting structure in the environment by tracking patterns present in the input. Recent experiments have revealed that infants possess remarkable statistical learning capabilities. Statistical learning may play a significant role in the precocious development of native language sound structure that occurs during the first year of life. During the second year, vocabulary development accelerates. The proposed experiments are motivated by the hypothesis that statistical learning about sounds lays a foundation for word learning. Thus, infants'ability to track statistical regularities may affect the ability to build a vocabulary. This research will examine the relation between individual differences in infants'vocabulary development and individual differences in statistical learning. The experiments will use measures of listening time and looking time to test infants'detection of novel statistical regularities, and to test their knowledge of native-language statistical regularities. Infants will participate speech, non-speech auditory, and visual statistical learning tasks in order to evaluate the coherence of statistical learning across domains. A label-learning task will also tap infants'ability to use native language statistical regularities to acquire new lexical items. In each experiment, infants'performance on experimental tasks will be integrated with measures of their real-world vocabulary development. This findings of this research promise to inform understanding of the underlying mechanism that contribute to individual differences in language acquisition. PUBLIC HEALTH RELEVANCE: The proposed research investigates the relation between individual differences in vocabulary development and how they relate to individual differences in statistical learning, a fundamental language acquisition mechanism. The findings from this project will influence understanding of typical language development and have potential to affect understanding of language delays and disorders. By focusing research on a mechanism that is thought to play a significant role in language acquisition, we may help to reveal potential deficits and means to identify infants who are at risk of developing lasting language problems.